Hot weather can quickly overcome a car in a number of ways. The coolant can be dissipated if not monitored regularly. The battery can be overtaxed with running the car and air conditioner excessively. Even the fuel system can work against you, flooding the engine before starting. The trick to solving the problem is to methodically go through potential problems to find the culprit.
Turn the key ignition on to see if the car still won't start. Look at the dash panel to confirm if the battery has enough juice to even display in the car or if it is completely dead with no electrical power whatsoever.
Open the car hood, and prop it up if necessary. Bump the battery with your shoe via good whack and try the ignition again (the bump may reset a faulty connection). Leave the key in the ignition in the "on" position and the radio turned on to hear it while checking the cables around the battery. Use a flashlight if it's too dark to see. Identify the last cable touched if the radio starts up.
Clear the engine from being flooded by pressing your foot all the way to the floor (this stops the throttle sensor from adding fuel at all). Start the ignition for not more than 15 seconds to air out the spark plugs, which may be fouled by sitting fuel. Let the car sit for a few seconds and try to start again (it should work if the problem is fouled plugs).
